This would be the seal in wax (mirror image)

Having seen the figure of Napoleon I and the way it was cast in bronze I am sure it cannot be an item that belonged to the French court and let alone the emperor, not even to an Imperial office. Most likely, it was a fancy seal of a Napoleon admirer who had his initials engraved.
Btw. I have a miniature painting of Lord Horatio Nelson, ivory under concave glass, original gilded box and several museums numbered tags on the back. Not for a single moment I thought it had belonged to Lady Hamilton or whoever was close to the admiral. Although, being boxed, the miniature was not meant to be displayed. Personal belongings of royalty, historical celebrities etc just do not fly around. They were popular and, depending of the country, reproduced in various ways.
Do not be disappointed, the seal is nice and worth collecting.
Best wishes